How do I reset the remote sensors

It is a known issue

Try first a general reset:
- remove the batteries from the clock (thus turning it Off.)
- remove the batteries from the outside sensor (if you are not aware that it has batteries, then perhaps it is not working because the batteries are no good any more! check that also.)
- wait 10 minutes with no power to the device.
- put batteries back in, power On again.
- hit Reset.
- hit Receive button.
- change the channel for reception from the outside sensor.
- change the channel on the outside sensor to match that channel.
- then set the time once more, once the remote temperature is sensed once again.

If this does not get the outside temperature reading working again, you may have to replace that temperature sensor.

https://www.google.com/search?q=Model+spc373

..

put it in the freezer and then try. you dont loose anything

Is the remote very far from the clock? I find that some of these remotes don't have very good range. Try bringing the remote close to the clock to see if you can get them to connect. Some of these type remotes have a reset button or an opening that you can push a paper clip into to reset. I usually try to find a location close enough to the unit so it will connect by still try to keep it out of the weather. I also included a link to the instructions:
http://www.hmdxaudio.com/media/documents/hmdxaudio/instructionbooks/HX-B320_EN_IB.pdf

The outside air temperature indicator's displayed temperature can be recalibrated. Press and hold the reset select button for 10 seconds . While you continue to hold the button, the display will scroll through temperature settings from +3 to -3. When the desired correction value appears on the display, release the button, and the recalibrated outside air temperature will be displayed. Each time a desired correction value is entered, it replaces the previous value. Give that a try mmkayyy:)

Contact Intermatic:
http://www.intermatic.com/en/CustomerSupport.aspx

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Bring the outside sensor inside. Take the batteries out of the sensor and out of the main unit. Wait 10 minutes. Put the batteries back in the remote sensor. Put the batteries back in the main unit. Do not touch any of the buttons. Wait 10 minutes. If the remote temperature is not showing within 10 minutes, try again. Once the remote temperature is showing, you can set the clock.

most likely the outside temp sensor is faulty it is located in front behind the grill

I would suspect that the connection to the outside temperature sensor is not good or the sensor itself is bad. Check the connection and clean and reattach as necessary. Otherwise replace the sensor. I think they're pretty reasonably priced.

The outside air temperature sensor for a 2000 Windstar is located under the front bumber on the passengers side. It is clearly visible if you lay down and look through the lower two air openings in the plastic bumper. It is the only electrical device in that area and it is made of black plastic.

you need to replace the ambient temperature sensor or do the math

there is a outside temperature sensor inside the lower front bumper
check wiring harness to sensor, or the sensor is defective